This paper reports the development of dual-modal all-optical photoacoustic microscopy (PAM) and photoacoustic viscoelasticity testing (PAVT) based on a common setup with tunable annular-beam excitation and wideband laser-vibrometer detection. For PAM, the annular beam is reduced to a small diameter to excite longitudinal bulk acoustic waves (BAWs) from light-absorbing targets buried in the sample, and the imaging quality is improved by a specified synthetic aperture focusing technique (SAFT). For PAVT, circularly converging surface acoustic waves (SAWs) are generated on the sample surface by annular beams with larger and different diameters. Both the induced BAWs and SAWs are detected at the center of the annular beam in a non-contact fashion by a broad-band laser vibrometer. Experiments have been conducted on the tissue-mimicking agar phantoms as well as animal tissues and have successfully demonstrated the initial concept of dual-modal all-optical PAM and PAVT.
This paper reports a new optically transparent focused P(VDF-TrFE) (poly(vinylidene fluoride-co-trifluoroethylene)) transducer for photoacoustic microscopy (PAM), which is fabricated by a new process based on pre-cutting and direct-lamination. Compared with the previous fabrication process, it is simpler, and makes it possible to achieve a high numerical aperture (NA) without stretching the (brittle) piezoelectric film. For demonstration, a prototype transducer has been fabricated with a 10-μm-thick 70/30 P(VDF-TrFE) film laminated onto a plano-concave glass lens with an NA of 0.64. Experimental characterization shows that the transducer has an optical transmittance of 88.6% (@ 532 nm), an acoustic center frequency and -3 dB bandwidth of 24 MHz and 29 MHz, respectively. Using the new optically transparent focused P(VDF-TrFE) transducer, an optical-resolution PAM (OR-PAM) imaging setup has been built and imaging experiments have been conducted on different targets. The experimental results show the optically transparent focused P(VDF-TrFE) transducer could be useful for the development of new PAM systems for different imaging applications.
Photoacoustic tomography (PAT) is a hybrid imaging technique, which is capable of providing abundant optical contrast and high spatial resolution at deep penetration depth. One fundamental challenge in current PAT system design is caused by the opaque structure of the ultrasound transducer arrays, which prevents effective light energy delivery onto the imaging target. To address this issue, we report a new optically-transparent PVDF (polyvinylidene fluoride) transducer array for PAT. It consists of a 1D array of 16 elements, each of which has a transparent window to allow the excitation laser pulses to directly pass through. As a result, the optical excitation and ultrasound detection zones are automatically aligned to improve the illumination condition and PA excitation efficiency. Its imaging performance, such as contrast, lateral resolution, and penetration depth has been characterized with optical phantoms. Preliminary ex-vivo PAT experiments on chicken breast tissues have been conducted to demonstrate its imaging capability on real biological samples. The experimental results show that the optically-transparent PVDF transducer array could provide a new solution for the miniaturization and clinical translation of handheld PAT systems.
As two important acoustic imaging modalities, photoacoustic microscopy (PAM) and ultrasound microscopy (UM) provide complementary functional and structural information on biological tissues. At penetration depths beyond the optical diffraction limit, the spatial resolution of both PAM and UM is determined acoustically by the receiving (focused) ultrasound transducer. To obtain good dual-modal imaging resolution, the transducer should have a high center frequency with a wide bandwidth. More importantly, a high acoustic numerical aperture (NA) should be maintained for receiving the PA and ultrasound signals, which is however difficult to achieve as the light blockage by the transducer is more likely to occur at higher NAs. In this paper, we report the dual-modal PAM and UM based on an optically-transparent focused PVDF transducer with a high NA of 0.64. The transducer has an acoustic center frequency and bandwidth of 36 MHz and 44 MHz, respectively. The acoustic focal diameter and zone are 37.8 μm and 210 μm, respectively. With a central transparent window, the excitation laser pulses can directly pass through the transducer to illuminate the target. This allows a high acoustic NA to be obtained without light blockage. For demonstration, co-registered 3D and 2D PAM/UM imaging experiments have been conducted on a twisted wire target in both water and chicken breast tissue, and in-vivo on a mouse tail, respectively. The imaging results show that high acoustic resolution and sensitivity can be achieved to resolve the target at different depths with a simple and compact dual-modal imaging setup
In photoacoustic microscopy (PAM), the ultrasound transducer plays a critical role in detecting the PA signals. However, conventional ultrasound transducers are optically opaque, which could hinder the effective delivery of the excitation laser onto the target. Recently, optically-transparent ultrasound transducers have been investigated to address this issue. Nevertheless, the transparent transducers demonstrated so far have either a small numerical aperture (NA) or narrow bandwidth, which limits their acoustic focal spot sizes and therefore achievable spatial resolutions. In this paper, we report a new focused transparent polyvinylidene fluoride (PVDF) transducer with a high NA of 0.64 and a wide acoustic pulseecho bandwidth of 120%. Experiment characterization shows that it has an acoustic center frequency and bandwidth of 36 MHz and 44 MHz, respectively. The acoustic focal diameter and zone are 37.8 μm and 210 μm, respectively. With the new transparent transducer, dual-modal acoustic-resolution PAM (AR-PAM) and pulse-echo ultrasound microscopy (PEUSM) have been demonstrated with a target consisting of black-ink-filled polyimide tubing buried in chicken breast at different depths. The imaging results show that both the (acoustic) lateral and axial resolutions can be maintained even at a penetration depth of larger than 3 mm.
This paper reports the development of a new charge amplification approach for photoacoustic tomography (PAT) based on parallel acoustic delay line (PADL) arrays. By using a PADL array to create different time delays, multiple-channel PA signals can be received simultaneously with a single-element transducer followed by single-channel DAQ electronics for image reconstruction. Unlike the conventional voltage amplifiers whose output voltage drops with increasing transducer capacitance, both theoretical analysis and experimental results have shown that the charge amplification can provide almost constant transducer-amplifier gain, which is not affected by the transducer capacitance. Therefore, it allows the use of a large single-element transducer to interface many PADLs without sacrificing the SNR of each channel. This opens the possibility of using large PADL arrays to achieve PAT with a wide field of view and high lateral resolution.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.